Oil sands (also called tar sands) are mixtures of organic matter, quartz sand, bitumen, and water that can either be mined or extracted in-situ using thermal recovery techniques. Typically, oil sands contain about 75% inorganic matter, 10% bitumen, 10% silt and clay, and 5% water. Bitumen is a heavy crude that does not flow naturally because of its low API (less than 10 degrees) and high sulfur content. The bitumen has high density, high viscosity, and high metal concentration. There is also a high carbon-to-hydrogen molecule count (i.e., oil sands are low in hydrogen). This thick, black, tar-like substance must be upgraded with an injection of hydrogen or by the removal of some of the carbon before it can be processed.
Oil sand products are sold in two forms: (1) as a raw bitumen that must be blended with a diluent (becoming a bit-blend) for transport and (2) as a synthetic crude oil (SCO) after being upgraded to constitute a light crude. The diluent used for blending is less viscous and often a by-product of natural gas, e.g., a natural gas condensate. The specifications for the bit blend (heavy oil) are 21.5 API and a 3.3% sulfur content and for the SCO (light oil) are 36 API and a 0.015% sulfur content. See Canada's Oil Sands, May 2004, p. 10.
Oil sands production measured only 1.3% of total world crude oil production in 2005. By 2025 it may reach 4.1% of total world production according to http://www.fas.org/sgp/crs/misc/RL34258.pdf.
Oil sands are either surface-mined or produced in-situ. Mining works best for deposits with overburden less than 75 meters thick. Mining requires a hydraulic or electric shovel that loads the sand into 400-ton trucks, which carry the material to a crusher to be mixed into a slurry. Using pumps and pipelines, the slurry is “hydro transported” to an extraction facility to extract bitumen. This process recovers about 90% of the bitumen.
The bitumen extraction process for mined oil sands in commercial use today separates the bitumen from the oil sands using warm water (75 degrees Fahrenheit) and chemicals. Extracting the oil from the sand after it is slurried consists of two main steps. First is the separation of bitumen in a primary separation vessel. Second, the bitumen material is sent to the froth tank for diluted froth treatment to recover the bitumen and reject the residual water and solids. The bitumen is treated either with a naphtha solvent or a paraffinic solvent to cause the solids to easily settle. The paraffinic treatment results in a product that can be shipped via pipeline and that is more easily blended with refinery feedstock. After processing, the bitumen oil is sold as raw bitumen or upgraded and sold as SCO.
Upgrading the bitumen uses the process of coking for carbon removal or hydrocracking for hydrogen addition. Coking is a common carbon removal technique that “cracks” the bitumen using heat and catalysts, producing light oils, natural gas, and coke (a solid carbon byproduct). The coking process is highly aromatic and produces a low quality product. The product must be converted in a refinery to a lighter gas and distillate. Hydrocracking also cracks the oil into light oils but produces substantially no coke byproduct. Hydrocracking requires natural gas for conversion to hydrogen. Hydrocracking, used often in Canada, better handles the aromatics. The resulting SCO has little residue, which help keep its market value high, equivalent to light crude.
Partial upgrading raises the API of the bitumen to 20-25 degrees for pipeline quality crude. A full upgrade would raise the API to between 30-43 degrees—closer to higher grade conventional crude. An integrated mining operation includes mining and upgrading. Many of the mining operations have an on-site upgrading facility, including those of Suncor and Syncrude. Suncor uses the coking process for upgrading, while Syncrude uses both coking and hydrocracking and Shell uses hydrocracking.
Water supply and waste water disposal are among the most serious concerns because of heavy use of water to extract bitumen from the sands. For an oil sands mining operation, about 2-3 barrels of water are used from the Athabasca River for each barrel of bitumen produced; but when recycled produced water is included, 0.5 barrels of “make-up” water is required, according to the Alberta Department of Energy. Oil sands projects currently divert 150 million cubic meters of water annually from the Athabasca River but are approved to use up to 350 million cubic meters. Concerns, however, arise over the inadequate flow of the river to maintain a healthy ecosystem and meet future needs of the oil sands industry. Additionally, mining operations impact freshwater aquifers by drawing down water to prevent pit flooding.
Wastewater tailings (a bitumen, sand, silt, and fine clay particles slurry) also known as “fluid fine tailings” are disposed in large ponds until the residue is used to fill mined-out pits. Seepage from the disposal ponds can result from erosion, breaching, and foundation creep. The principal environmental threat is the migration of tails to a groundwater system and leaks that might contaminate the soil and surface water. The tailings are expected to reach 1 billion cubic meters by 2020. Impounding the tailings will continue to be an issue even after efforts are made to use alternative extraction technology that minimizes the amount of tails. Tailings management criteria were established by the Alberta Energy and Utilities Board/Canadian Environmental Assessment Agency in June 2005. Ongoing extensive research by the Canadian Oil Sands Network for Research and Development (CONRAD) is focused on the consolidation of wastewater tailings, detoxifying tailings water ponds, and reprocessing tailings.
Waterless approaches using hydrocarbon solvent extraction technology have been examined. These approaches offer a pathway to obtaining oil from oil sands that could be potentially low energy, water free, and environmentally superior to the current water-based technology.
U.S. Pat. No. 3,475,318 to Gable et al. is directed to a method of selectively removing oil from oil sands by solvent extraction with subsequent solvent recovery. The extraction solvent consists of a saturated hydrocarbon of from 5 to 9 carbon atoms per molecule. Volatile saturated solvents such as heptane, hexane and non-aromatic gasoline are used to selectively remove saturated and aromatic components of the bitumen from the oil sand, while leaving the corresponding asphaltenes on the sand. In order to remove the asphaltenes for potential use as process fuel, an aromatic such as benzene or toluene is added to the solvent at a concentration of from 2 to 20 weight percent.
U.S. Pat. No. 4,347,118 to Funk et al. is directed to a solvent extraction process for tar sands, which uses a low boiling solvent having a normal boiling point of from 20° C. to 70° C. to extract the bitumen from the tar sands. The solvent is mixed with tar sands in a dissolution zone at a solvent:bitumen weight ratio of from about 0.5:1 to 2:1. This mixture is passed to a separation zone containing a classifier and countercurrent extraction column, which are used to separate bitumen and inorganic fines from extracted sand. The extracted sand is introduced into a first fluid-bed drying zone fluidized by heated solvent vapors, to remove unbound solvent from extracted sand and lower the water content of the sand to less than about 2 wt. %. The treated sand is then passed into a second fluid-bed drying zone fluidized by a heated inert gas to remove bound solvent. Recovered solvent is recycled to the dissolution zone.
U.S. Pat. No. 7,985,333 to Duyvesteyn is directed to a method for obtaining bitumen from tar sands. The method includes using multiple solvent extraction or leaching steps to separate the bitumen from the tar sands. A light aromatic solvent such as toluene, xylene, kerosene, diesel (including biodiesel), gas oil, light distillate, commercially available aromatic solvents such as Solvesso 100, 150, and 200, naphtha, benzene and aromatic alcohols can be used as a first solvent. A second hydrocarbon solvent, which includes aliphatic compounds having 3 to 9 carbon atoms and liquefied petroleum gas, can also be used in the extraction process.
U.S. Patent Pub. No. 2009/0294332 to Ryu discloses an oil extraction process that uses an extraction chamber and a hydrocarbon solvent rather than water to extract the oil from oil sand. The solvent is sprayed or otherwise injected onto the oil-bearing product, to leach oil out of the solid product resulting in a composition comprising a mixture of oil and solvent, which is conveyed to an oil-solvent separation chamber.
U.S. Patent Pub. No. 2010/0130386 to Chakrabarty discloses the use of a solvent for bitumen extraction. The solvent includes (a) a polar component, the polar component being a compound comprising a non-terminal carbonyl group; and (b) a non-polar component, the non-polar component being a substantially aliphatic substantially non-halogenated alkane. The solvent has a Hansen hydrogen bonding parameter of 0.3 to 1.7 and/or a volume ratio of (a):(b) in the range of 10:90 to 50:50.
U.S. Patent Pub. No. 2011/0094961 to Phillips discloses a process for separating a solute from a solute-bearing material. The solute can be bitumen and the solute-bearing material can be oil sand. A substantial amount of the bitumen can be extracted from the oil sand by contacting particles of the oil sand with globules of a hydrocarbon extraction solvent. The hydrocarbon extraction solvent is a C1-C5 hydrocarbon. The particle size of the oil sand and the globule size of the extraction solvent are balanced such that little if any bitumen or extraction solvent remains in the oil sand.
U.S. Patent Pub. No. 2012/0261313 to Diefenthal et al. is directed to a process for producing a crude oil composition from oil sand that uses a solvent comprised of a hydrocarbon mixture. The solvent is injected into a vessel and the oil sand is supplied to the vessel such that the solvent and oil sand contact one another in the vessel, i.e., contact zone of the vessel. The process is carried out such that not greater than 80 wt % of the bitumen is removed from the supplied oil sand, with the removal being controlled by the Hansen solubility blend parameters of the solvent and the vapor condition of the solvent in the contact zone. The extracted oil and at least a portion of the solvent are removed from the vessel for further processing as may be desired.
U.S. Patent Pub. No. 2013/0220890 to Ploemen et al. is directed to a method for extracting bitumen from an oil sand stream. The oil sand stream is contacted with a liquid comprising a solvent to obtain a solvent-diluted oil sand slurry. The solvent-diluted oil sand slurry is separated to obtain a solids-depleted stream and a solids-enriched stream. The solvent-to-bitumen weight ratio (S/B) of the solids-enriched stream is increased to produce a solids-enriched stream having an increased S/B weight ratio and a liquid stream. The solids-enriched stream having an increased S/B weight ratio is filtered to obtain the bitumen-depleted sand. The solvent can include aromatic hydrocarbon solvents and saturated or unsaturated aliphatic hydrocarbon solvents.
There is a continuing need for waterless approaches using hydrocarbon solvent extraction technology to extract crude oil and bitumen products from oil sand. There is a particular need for obtaining high quality crude oil and obtaining relatively dry tailings from the hydrocarbon extraction processes.